1. Field of the Invention
This invention relates to ophthalmic devices, such as contact lenses and intraocular implants, and particularly contact lenses of a block copolymer containing polysiloxane and polyoxyalkylene oxide units possessing an advantageous blend of desirable properties including (a) high oxygen permeability, (b) good wettability, (c) flexibility, (d) optical clarity, and e) a substantial lack of aqueous swellability in the ocular environment of use.
2. Background Art
The use of siloxane containing materials of various types in the fabrication of ophthalmic devices is well known.
Thus, in U.S. Pat. Nos. 3,996,187; 3,996,189; 3,341,490 and 3,228,741 there are described contact lenses fabricated from poly (organosiloxanes) containing fillers. While such lenses are generally soft and of high oxygen permeability, the use of fillers such as silica, is indicated in order to increase the otherwise generally poor tear strength and tensile strength. Also, such silicone rubber lenses are characteristically both hydrophobic and lipophilic.
U.S. Pat. No. 3,808,178 discloses hard contact lenses fabricated from copolymers of a polysiloxanylakyl acrylate or methacrylate ester and an alkyl acrylate or metacylate ester. The monomers and polymers of the patent are hydrophobic and are incompatible with hydrophilic materials such as hydroxyethyl methacrylate. While the disclosed lenses have increased oxygen permeability, they are rigid.
U.S. Pat. No. 4,136,250 discloses hydrogels of a copolymer of about 20 to about 90% of a hydrophilic (or mixture of hydrophilic and hydrophobic) monomer and about 10 to about 80% of a polyolefinic siloxane macromer which can be used to fabricate a contact lens. Typically, such hydrogels are recited to possess a degree of swelling of about 10 to about 12%. It has been found, however, that the presence of substantial amounts of water in such hydrogels limits the oxygen permeability of such materials.
U.S. Pat. No. 4,153,641 relates, in relevant part, to contact lenses fabricated from a polymer of a polyorganosiloxane terminated with vinylic groups, or copolymers thereof with other monomers. The exemplified products therein are hydrophobic in nature.
U.S. Pat. No. 4,486,577 relates to copolymers of about 8 to 70% of a polysiloxane macromer containing at least two vinyl groups and 30-92% of a monomer which is at least predominantly water insoluble to make polymers useful, for example, as contact lenses.
Generally, such prior art contact lens compositions are either insufficiently hydrophilic in terms of surface wettability to be acceptable to the contact lens profession, even though they may possess high oxygen permeability, or such contact lenses are of acceptable wettability but the hydrophilicity is coupled with water swellability, which tends to limit optimum oxygen permeability.
It is an object of the present invention to overcome these and other disadvantages of the art by providing ophthalmic devices, such as contact lenses and corneal implants, possessing a high degree of surface wettability but which are substantially non-swellable in the aqueous environment of use, and possessing a high degree of oxygen permeability by employing a crosslinked block polymer containing polysiloxane and polyalkylene oxide units.
A further object of the invention is to provide a method of correcting visual defects in the form of refractive errors by fitting to the patient's eye in need of the same, a corrective contact lens of such polymer. These and other objects of the invention are apparent from the following detailed description of the invention.